Viruses that infect immune cells (such as T-cell, B-cell, dendritic cell, monocyte, or macrophage) include porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type II (PCV2), and human immunodeficiency virus (HIV). The immune cells cannot evoke immunization responses but carry the viruses. The animals that have been infected by these viruses can be easily infected by other pathogens. Porcine reproductive and respiratory syndrome virus (PRRSV) results in high losses in animal husbandry every year. Not only swine but ducks can be infected by PRRSV as well. Generally, the animals infected by the virus have no significant symptoms, but the immunity of the infected animals is reduced. This virus infects macrophages (in the alveolar and spleen), brain microglia and monocytes, and can exist in the blood and organs of the infected animals. This leads to a decrease of weight gain and an increase in the death rate due to the secondary infection.
U.S. Pat. No. 7,595,054 discloses a fusion antigen used as a subunit vaccine, in which a single antigen moieity selected from a region of ORF1b or a region of ORF7 is fused between a Pseudomnoas exotoxin A polypeptide that is devoide of the cytotoxic domain III, i.e., PE (ΔIII), and an endoplasmic retiuclum retention sequence.
A vaccine composition named “PRRSFREE™” by Reber Genetics Co. Ltd. comprises four separate PRRS antigens, which are designated as D, M, R, and P, respectively. These four PRRS antigens were respectively expressed by four separate vectors using the design disclosed in U.S. Pat. No. 7,595,054, and were found effective in inducing cell-mediated and humoral immune responses in animals.